How much does it cost to fix Alpha error code C1?

Typical repair cost for the Alpha C1 fault is £120-220 including labour.

C1 High

Alpha C1 Fault Code

Q: What does the Alpha C1 fault code mean?

Your boiler has stopped working because it is unable to accurately measure the temperature of the water returning to it, so it has shut down as a precaution.

The Alpha C1 fault code means: your boiler has stopped working because it is unable to accurately measure the temperature of the water returning to it, so it has shut down as a precaution.. It appears on 2 Alpha models in our database.

Technical description: Primary return temperature sensor faulty (no heating); cold resistance approx. 12-14 kohms

Typical repair cost £120-220 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Alpha models that show the C1 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Alpha C1 fault code information on this page is sourced and cross-checked against the official Alpha service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026